Insert line after match using sed

sedshell

For some reason I can't seem to find a straightforward answer to this and I'm on a bit of a time crunch at the moment. How would I go about inserting a choice line of text after the first line matching a specific string using the sed command. I have …

CLIENTSCRIPT="foo"
CLIENTFILE="bar"

And I want insert a line after the CLIENTSCRIPT= line resulting in …

CLIENTSCRIPT="foo"
CLIENTSCRIPT2="hello"
CLIENTFILE="bar"

Best Answer

Try doing this using GNU sed:

sed '/CLIENTSCRIPT="foo"/a CLIENTSCRIPT2="hello"' file

if you want to substitute in-place, use

sed -i '/CLIENTSCRIPT="foo"/a CLIENTSCRIPT2="hello"' file

Output

CLIENTSCRIPT="foo"
CLIENTSCRIPT2="hello"
CLIENTFILE="bar"

Doc

see sed doc and search \a (append)

Related Solutions

Bash – How to remove the first line of a text file using bash/sed script

Try tail:

tail -n +2 "$FILE"

-n x: Just print the last x lines. tail -n 5 would give you the last 5 lines of the input. The + sign kind of inverts the argument and make tail print anything but the first x-1 lines. tail -n +1 would print the whole file, tail -n +2 everything but the first line, etc.

GNU tail is much faster than sed. tail is also available on BSD and the -n +2 flag is consistent across both tools. Check the FreeBSD or OS X man pages for more.

The BSD version can be much slower than sed, though. I wonder how they managed that; tail should just read a file line by line while sed does pretty complex operations involving interpreting a script, applying regular expressions and the like.

Note: You may be tempted to use

# THIS WILL GIVE YOU AN EMPTY FILE!
tail -n +2 "$FILE" > "$FILE"

but this will give you an empty file. The reason is that the redirection (>) happens before tail is invoked by the shell:

Shell truncates file $FILE
Shell creates a new process for tail
Shell redirects stdout of the tail process to $FILE
tail reads from the now empty $FILE

If you want to remove the first line inside the file, you should use:

tail -n +2 "$FILE" > "$FILE.tmp" && mv "$FILE.tmp" "$FILE"

The && will make sure that the file doesn't get overwritten when there is a problem.

Shell command to sum integers, one per line

Bit of awk should do it?

awk '{s+=$1} END {print s}' mydatafile

Note: some versions of awk have some odd behaviours if you are going to be adding anything exceeding 2^31 (2147483647). See comments for more background. One suggestion is to use printf rather than print:

awk '{s+=$1} END {printf "%.0f", s}' mydatafile

Best Answer

Output

Doc

Related Solutions

Bash – How to remove the first line of a text file using bash/sed script

Shell command to sum integers, one per line

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